There is a desire to improve internal combustion engines which are operated with fossil fuels to the effect that the limiting values for emissions and the fuel consumption are reduced. As a result, the mechanical design of an internal combustion engine is becoming ever more complex. In particular, the efficiency of the internal combustion engine can be improved by the way in which the air mass is fed into a cylinder. Depending on the design of the engine, for example complex camshaft adjustment systems for adjusting the stroke and the phase of the inlet and outlet valves can be controlled in such a way that filling losses of the cylinders are reduced. For example, inlet and outlet valves of various cylinders can also be actuated differently.
In the field of engine control, the filling of the cylinders with fresh air is usually determined by modeling an intake section, i.e. by means of what is referred to as a container model. The calculation of the quantity of fuel to be injected is carried out for all the cylinders in the same way with a model-based value. Differences between the individual cylinders can be taken into account here only at high cost. In particular, in the case of rapid load changes, during which the filling changes markedly from one working cycle to the other or during the active adjustment of the camshaft phase or the valve stroke, the correction requires very complex functions and calibration of the characteristic diagrams. Owing to the mechanical design of the intake section and a multiplicity of variables in the valve drive, in particular in the case of the valve stroke adjustment systems, which adjust continuously and in some cases on a cylinder-specific basis, differences can come about between specific cylinders during the taking in of fresh air. For example, this can also be caused by pulsation in the intake manifold. In this context, in particular mechanical component tolerances are an influencing factor in series fabrication and can lead to fresh air supply faults of the individual cylinders, and cannot be excluded even with the best application.
The large variability of the individual valves also leads to a situation in which in the case of dynamic changes in load the sucked-in air mass in the cylinders or the air mass in the cylinders which is blown in by the turbocharger can be increasingly difficult to determine with the model mentioned above.
For example, it is also possible to use calculation models which are based on measurement data of intake manifold pressure sensors, air mass meters, temperature sensors or lambda probe measured values. For example, the filling in a cylinder, composed of fresh air, residual gas and fuel according to Jippa can be determined by means of a filling equivalent, wherein the filling equivalent is determined based on a cylinder pressure during a compression phase of the cylinder. The total gas mass located in the cylinder can be inferred from the filling equivalent by using, in addition to the cylinder pressure profile, various further characteristic parameters such as, for example, the engine rotational speed, the air ratio, the coolant temperature, the ambient temperature and the ambient pressure (Jippa, Kai-Nicolas: “Online-capable, thermodynamic approaches for evaluating cylinder pressure profiles”, dissertation, University of Stuttgart, 2002)
For this measurement of fresh air in a cylinder using the measurement of the filling and using the filling equivalent, complex models are necessary, inter alia owing to the multiplicity of required parameters, said models resulting in an extremely complex engine control system. Furthermore, a multiplicity of additional sensors are necessary.